How to Handle Inconsistent JSON Fields: Strings vs. Arrays?

Handling Inconsistent JSON Fields: A Case of Strings vs. Arrays

When dealing with JSON data that is not entirely consistent, challenges may arise in the unmarshalling process. This can occur when a particular field in the JSON varies in its format, posing difficulties for the unmarshalling process.

The Problem:

Consider the following scenario:

type MyListItem struct {
    Date  string `json:"date"`
    DisplayName       string `json:"display_name"`
}

type MyListings struct {
    CLItems []MyListItem `json:"myitems"`
}

The JSON data has a field called "display_name," which is expected to be a string. However, in some cases, it can also be an array of strings. This inconsistency complicates the unmarshalling process, leading to errors.

The Solution:

To overcome this challenge, we can leverage two techniques:

1. Utilizing json.RawMessage: Capture the problematic field as a json.RawMessage type.
2. Employing the JSON "-" Name: Define the "DisplayName" field as "-" in the JSON decoder to exclude it from the unmarshalling process.

Updated Code:

type MyListItem struct {
    Date           string          `json:"date"`
    RawDisplayName json.RawMessage `json:"display_name"`
    DisplayName    []string        `json:"-"`
}

Unmarshalling the JSON:

Unmarshalling the top-level JSON:

var li MyListItem
if err := json.Unmarshal(data, &li); err != nil {
    // handle error
}

Extracting the "DisplayName" field depending on its type:

if len(li.RawDisplayName) > 0 {
    switch li.RawDisplayName[0] {
    case '"':
        if err := json.Unmarshal(li.RawDisplayName, &li.DisplayName); err != nil {
            // handle error
        }
    case '[':
        var s []string
        if err := json.Unmarshal(li.RawDisplayName, &s); err != nil {
            // handle error
        }
        li.DisplayName = strings.Join(s, "&&")
    }
}

Example:

var listings MyListings
if err := json.Unmarshal([]byte(data), &listings); err != nil {
    // handle error
}
for i := range listings.CLItems {
    li := &listings.CLItems[i]
    if len(li.RawDisplayName) > 0 {
        switch li.RawDisplayName[0] {
        case '"':
            if err := json.Unmarshal(li.RawDisplayName, &li.DisplayName); err != nil {
                // handle error
            }
        case '[':
            var s []string
            if err := json.Unmarshal(li.RawDisplayName, &s); err != nil {
                // handle error
            }
            li.DisplayName = strings.Join(s, "&&")
        }
    }
}

By adopting these techniques, you can effectively handle inconsistent JSON fields, ensuring proper data extraction and manipulation in your application.

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